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Abstract:

A polymer membrane for water treatment, characterized in comprising a
hollow fiber membrane having a self-supporting design composed of the
substantially single principal structural material, with an outer
diameter of 3.6 mm to 10 mm and a ratio of outer diameter to thickness,
SDR, of 3.6 to 34.

Claims:

1-15. (canceled)

16. A polymer membrane for water treatment comprising a hollow fiber
membrane having a self-supporting design composed of vinyl chloride resin
as a substantially single principal structural material, with an outer
diameter of 3.6 mm to 10 mm and a ratio of outer diameter to thickness,
SDR, of 5.8 to 34.

17. The polymer membrane for water treatment according to claim 16,
wherein in the cross-section in the radial direction of the hollow fiber
membrane; (a) the porosity based on the hollow fiber membrane
cross-sectional area is 30-85%, (b) the pores with a short axis dimension
of 10-100 μm are 80% or more of the total pore surface area, and (c)
there is a laminar distribution of pores constituting the innermost
layer, inner layer, outer layer and outermost layer from the center in
the radial direction, and the long axis dimension of the pores in each of
the inner layer and outer layer comprises 20-50% of the thickness,
respectively, while the long axis dimension of the pores in each of the
innermost layer and outermost layer comprises 0-20% of the thickness,
respectively.

18. The polymer membrane for water treatment according to claim 16,
wherein the polymer membrane has the fractionation property of an
ultrafiltration membrane or a microfiltration membrane.

19. The polymer membrane for water treatment according to claim 17,
wherein the polymer membrane has the fractionation property of an
ultrafiltration membrane or a microfiltration membrane.

20. The polymer membrane for water treatment according to claim 16,
wherein the polymer membrane has; an internal pressure resistance of 0.3
MPa or greater, an external pressure resistance of 0.1 MPa or greater,
and pure water flux of 100 L/m2hratm or greater.

21. The polymer membrane for water treatment according to claim 16,
wherein the main structural material is poly(vinyl chloride), chlorinated
poly(vinyl chloride), or a vinyl chloride-chlorinated vinyl chloride
copolymer.

22. The polymer membrane for water treatment according to claim 16,
wherein the degree of polymerization of the vinyl chloride resin is
250-3000.

23. The polymer membrane for water treatment according to claim 16,
wherein the chlorine content in the vinyl chloride resin is 56.7 to
73.2%.

24. The polymer membrane for water treatment according to claim 16,
wherein the mass ratio of vinyl chloride monomer units in the vinyl
chloride resin amounts to 50-99 mass %.

25. A method for the manufacture of a polymer membrane for water
treatment comprising; preparing a resin solution from vinyl chloride
resin as a substantially single principal structural material, and
coagulating the resin solution by discharging from a discharge port into
a coagulation tank at within .+-.30.degree. of horizontal with respect to
the ground, the polymer membrane is a hollow fiber membrane having a
self-supporting design composed of vinyl chloride resin as a
substantially single principal structural material, with an outer
diameter of 3.6 mm to 10 mm and a ratio of outer diameter to thickness,
SDR, of 5.8 to 34.

26. The method for the manufacture of a polymer membrane for water
treatment according to claim 25 comprising; coagulating the resin
solution by discharging from a discharge port in which a discharge
direction of the resin solution is in a horizontal direction with respect
to the ground into a coagulation tank.

27. The method for the manufacture of a polymer membrane for water
treatment according to claim 25 that uses a spinneret provided with a
discharge port, where the discharge port discharges the resin solution in
an immersed state into a coagulation tank that contains a non-solvent.

28. The method for the manufacture of a polymer membrane for water
treatment according to claim 26 that uses a spinneret provided with a
discharge port, where the discharge port discharges the resin solution in
an immersed state into a coagulation tank that contains a non-solvent.

29. The method for the manufacture of a polymer membrane for water
treatment according to claim 25, which further comprises; cutting the
membrane obtained within the tank, or cutting the membrane outside the
tank at a position higher than the discharge port.

30. The method for the manufacture of a polymer membrane for water
treatment according to claim 25, wherein the difference in specific
gravity between the resin solution and the non-solvent is within 1.0.

31. A method for water treatment characterized in that the polymer
membrane for water treatment according to claim 16 is used as a
separation membrane.

32. A method for water treatment characterized in separating water by
passing microbiological treated wastewater using activated sludge inside
the polymer membrane for water treatment according to claim 16.

33. The method for the manufacture of a polymer membrane for water
treatment according to claim 25, using a spinneret provided with a
discharge port, after preparing the resin solution, submerging the
spinneret into a coagulation tank while discharging the resin solution
previously from the spinneret in the air, and discharging the resin
solution into a coagulation tank.

34. A method for the manufacture of a polymer membrane for water
treatment comprising; preparing a resin solution from a substantially
single principal structural material, using a spinneret provided with a
discharge port, after preparing the resin solution, submerging the
spinneret into a coagulation tank while discharging the resin solution
previously from the spinneret in the air, and coagulating the resin
solution by discharging from a discharge port into a coagulation tank at
within .+-.30.degree. of horizontal with respect to the ground, the
polymer membrane is a hollow fiber membrane having a self-supporting
design composed of the substantially single principal structural
material, with an outer diameter of 3.6 mm to 10 mm and a ratio of outer
diameter to thickness, SDR, of 5.8 to 34.

Description:

TECHNICAL FIELD

[0001] The present invention relates to a polymer membrane for water
treatment a method for the manufacture of same, and a water treatment
method.

BACKGROUND ART

[0002] Conventionally, polymer membranes for water treatment are used for
purifying water, for example, for removing turbidity from river water and
groundwater, clarification of industrial water, treatment of wastewater
and sewage, and as a pretreatment for seawater desalination, and the
like.

[0003] Usually, such polymer membranes for water treatment are used as
separation membranes in water treatment devices that utilize porous
hollow fiber membranes formed from various polymer materials such as, for
example, polystyrene (PS), poly(vinylidene fluoride) (PVDF), polyethylene
(PE), cellulose acetate (CA), polyacrylonitrile (PAN), poly(vinyl
alcohol) (PVA), polyimide (PI), and the like. In particular, polysulfone
resins are frequently used due to their superior mechanical and chemical
properties such as heat resistance, acid resistance, alkali resistance,
and the like, and from the additional perspective of the ease of making a
membrane.

[0004] By supplying contaminated water under pressure to micropores,
porous hollow fiber membranes can remove contaminating substances from
water by capturing only contaminating substances of a certain size or
larger. In general, examples of the properties that are required in such
polymer membranes for water treatment, in addition to the goal of
separation characteristics, include having superior water permeability
and superior physical strength, high stability toward a variety of
chemical substances (namely, chemical resistance), less likelihood of
adhesion of impurities during filtration (namely, superior antifouling
properties), and the like.

[0005] For example, cellulose acetate fiber hollow-fiber separation
membranes have been proposed that have comparatively high water
permeability and are less likely to become contaminated even when used
for long periods (see Patent Document 1).

[0006] However, this cellulose acetate hollow-fiber separation membrane
has low mechanical strength and its chemical resistance is inadequate.
Consequently, there is a problem in that when the separation membrane
becomes contaminated, cleaning employs physical means or chemical means
using chemical products and is extremely difficult.

[0007] Additionally, polymer membranes for water treatment have been
proposed using hollow fiber membranes formed from poly(vinylidene
fluoride) resin that have both superior physical strength and chemical
resistance (see Patent Document 2). This polymer membrane for water
treatment can be used by direct immersion in an aeration tank, and can be
cleaned using various chemical agents even when contaminated.

[0009] The use of submersion-type MBRs (membrane bioreactors) have
frequently been used in sewer water treatment in recent years (see Patent
Documents 3 and 4). This submersion-type MBR is a method to obtain
treated water by suction filtration using hollow fiber-type or flat-type
water treatment membranes immersed in a biological water treatment tank,
and the membrane surfaces are cleaned by continuous aeration to prevent
the reduction in filtration efficiency when contaminants are deposited on
the outer surface of the membrane.

[0010] However, the energy for the required aeration in immersion-type
MBRs is associated with substantial electrical energy costs, which causes
an increase in running costs.

[0011] In addition, depending on the particular application, water
treatment is differentiated into inside-out filtration and outside-in
filtration. For example, when the filtered liquid is already high-purity
tap water, inside-out filtration is used and high-pressure water is
supplied to hollow-fiber membranes with a small inner diameter. In this
way, water treatment at a high filtration rate is possible. On the other
hand, to prevent the occlusion inside the membrane by turbidity
components when high-turbidity water is filtered, the operational method
used for carrying out the water treatment employs low pressure using
either a tubular membrane with a large pore diameter made from a
composite material on a support frame or a flat membrane, and either an
air flow or water flow is supplied to the membrane outer surface to
prevent the deposition of the turbidity components on the membrane
surface.

[0012] Furthermore, an inside-out type (outside the tank type) MBR has
been proposed in which bio-treated water flows into a hollow-fiber
membrane that is installed in a water bio-treatment tank and the
filtration is carried out using internal pressure. In a water treatment
membrane module that employs this inside-out mode MBR, a tubular-shaped
water treatment membrane with an inner diameter of about 5 to 10 mm is
used so that no occlusion will occur due to deposition of solids at the
module end surface caused by bio-treated water that contains solids of
varying sizes.

[0013] However, the treatment rate frequently cannot be accommodated due
to problems with pressure resistance with flat-membrane filtration, and
equipment other than the raw water pump and energy are required as a
solution for preventing the deposition of turbidity components on the
membrane surface.

[0014] Additionally, as a consequence of the increase in inner diameter of
the water treatment membrane, treatment using a tubular membrane requires
a firm support frame or an increase in membrane thickness to reduce the
resistance to internal pressure during treatment. On the other hand, when
using a support frame, generally back-pressure washing (backwashing) of
the hollow-fiber membrane is carried out when the treatment rate
decreases due to deposition of contaminants such as turbidity components
and the like on the membrane surface, but damage can readily occur in
this way when the tubular membrane that is attached to the support frame
peels away. In particular, backwashing is practically impossible in an
inside-out filtration-type tubular membrane that is suitable for the
treatment of water with high suspended substances content. Consequently,
in methods other than backwashing, a sponge ball is used to prevent a
decrease in water permeation rate, a high internal flow rate is
maintained, and the like, complication of the system and an increase in
energy expenditures is currently unavoidable.

[0015] Moreover, when the water treatment membrane thickness is increased,
this leads to the new problem of decreasing the footprint efficiency
based on the water treatment rate.

[0016] Furthermore, in a method for manufacturing porous hollow-fiber
membranes, conventionally, a resin solution comprising resin and solvent
passes into a double-tube-type mold and a non-solvent is used to direct
coagulation water to an interior part that will become a hollow part, and
the non-solvent induced phase separation method (NIPS method) is applied
to carry out phase separation by immersion of the outer part in a
coagulation bath (for example, Patent Document 5). In this method, the
resin solution leaving the mold is once brought into contact with air,
and the solvent in the resin solution evaporates to form a skin layer.
For this reason, the resin solution is submersed in the coagulation tank
by dropping vertically due to gravity, and thereafter the membrane
obtained by coagulation of the resin component in the coagulation tank is
passed along a guide such as a roller, transferred to a different machine
direction, and finally positioned horizontally in the machine direction
and cut.

[0017] However, making the pore diameter in the porous hollow-fiber
membrane larger can produce cracks, swelling, warping, uneven
thicknesses, and the like. In addition, the take-up becomes difficult,
and the manufacture of homogeneous hollow-fiber membranes, such as with a
flattened membrane shape or the like, becomes extremely difficult, with
the result that there are also problems in obtaining a polymer membrane
for water treatment in which the abovementioned characteristics can be
adequately achieved.

[0023] As mentioned above, there is a strong demand for polymer membranes
for water treatment that can satisfy all the requirements such as having
superior water permeability, superior physical strength, high chemical
resistance, and superior antifouling properties.

[0024] Additionally, it is desirable to establish a method for manufacture
wherein a membrane that can adequately achieve such characteristics can
be manufactured easily and reliably.

[0025] Taking account of the aforementioned problems, the object of the
present invention is to provide a polymer membrane for water treatment
that maintains mechanical strength, water permeability, and the like,
while increasing the water treatment efficiency, and a method for
manufacture of a polymer membrane for water treatment wherein the
manufacture is easy and reliable, and a water treatment method that can
realize efficient water treatment and maintenance.

Means to Solve the Problem

[0026] As the result of diligent study of increasing footprint efficiency
as applied to an inside-out mode MBR, by focusing on the strength of the
water treatment membrane and how to improve same, the present inventors
discovered that they could obtain a water treatment membrane that
suitably achieved the abovementioned tradeoff between the two
characteristics.

[0027] In other words, using an appropriate design for the SDR value
specified by the ratio between the outer diameter and the thickness, and
an appropriate design for the porosity that is apparent from the
cross-section, they discovered they could obtain a water treatment
membrane with an inner diameter larger than conventional hollow-fiber
membranes and could obtain adequate resistance to the internal and
external pressures associated with filtration operations.

[0028] Furthermore, in the membrane manufacture steps, as a result of
conducting a diligent study of the reactions and actions of a resin
solution in a coagulation tank, the method of transfer of the membrane
obtained, and the like, the present inventors discovered a method by
which they could simply and reliably manufacture a membrane that would
adequately achieve the abovementioned characteristics in a spinning state
under specified conditions and/or with transfer/recovery of the membrane
under specified conditions, and thereby accomplished the present
invention.

[0029] That is, polymer membrane for water treatment according to the
present invention, characterizes in comprising a hollow fiber membrane
having a self-supporting design composed of the substantially single
principal structural material,

[0030] with an outer diameter of 3.6 mm to 10 mm and

[0031] a ratio of outer diameter to thickness, SDR, of 3.6 to 34.

[0032] Such polymer membrane for water treatment preferably has one or
more below.

[0033] In that in the cross-section in the radial direction of the hollow
fiber membrane;

[0034] (a) the porosity based on the hollow fiber membrane cross-sectional
area is 30-85%,

[0035] (b) the pores with a short axis dimension of 10-100 μm are 80%
or more of the total pore surface area, and

[0036] (c) there is a laminar distribution from the center in the radial
direction of the innermost layer, inner layer, outer layer and outermost
layer, and the long axis dimension of the pores in each of the inner
layer and outer layer comprises 20-50% of the thickness, while the long
axis dimension of the pores in each of the innermost layer and outermost
layer comprises 0-20% of the thickness.

[0037] The polymer membrane has the fractionation property of an
ultrafiltration membrane or a microfiltration membrane.

[0046] A method for the manufacture of a polymer membrane for water
treatment has;

[0047] preparing a resin solution from a substantially single material,
and

[0048] coagulating the resin solution by discharging from a discharge port
into a coagulation tank at within ±30° of horizontal with
respect to the ground.

[0049] Such method for the manufacture preferably has one or more below.

[0050] The method has

[0051] preparing a resin solution composed of the substantially single
principal structural material, and

[0052] coagulating the resin solution by discharging from a discharge port
in which a discharge direction of the resin solution is in a horizontal
direction with respect to the ground into a coagulation tank.

[0053] Using a spinneret provided with a discharge port, where the
discharge port discharges the resin solution in an immersed state into a
coagulation tank that contains a non-solvent.

[0054] The method further has;

[0055] cutting the membrane obtained within the tank, or

[0056] cutting the membrane outside the tank at a position higher than the
discharge port.

[0057] The difference in specific gravity between the resin solution and
the non-solvent is within 1.0.

[0058] A method for water treatment of the present invention characterizes
that the polymer membrane for water treatment described above is used as
a separation membrane or that separating water is performed by passing
microbiological treated wastewater using activated sludge inside the
polymer membrane for water treatment described above.

Effect of the Invention

[0059] According to the present invention, the present invention is
possible to provide a polymer membrane for water treatment that maintains
mechanical strength, water permeability, and the like, while increasing
the water treatment efficiency.

[0060] Also, using the method of the present invention is possible to
manufacture the polymer membrane for water treatment which can be
successfully satisfy the above properties.

[0061] Further, using the polymer membrane for water treatment can realize
efficient water treatment and maintenance.

BRIEF EXPLANATION OF DIAGRAMS

[0062] FIG. 1 A schematic diagram that describes a cross-section along the
radial direction of a polymer membrane for water treatment of the present
invention.

[0063] FIG. 2 A conceptual diagram that describes an inside-out mode MBR
using a water treatment unit equipped with a polymer membrane for water
treatment of the present invention.

[0064] FIG. 3 A schematic diagram that describes the discharge angle for
the resin solution in a method for manufacturing a polymer membrane for
water treatment of the present invention.

[0065] FIG. 4 A schematic diagram that describes the steps from discharge
of the resin solution to cutting of the membrane in a method for
manufacturing a polymer membrane for water treatment of the present
invention.

[0066] FIG. 5 A schematic diagram that describes the take-up of the resin
solution in a comparative example.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0067] The polymer membrane for water treatment of the present invention
is primarily a membrane composed of a hollow-fiber membrane that has a
self-supporting structure using a substantially single principal
structural material.

[0068] (Form/Structure)

[0069] In other words, the polymer membrane for water treatment of the
present invention is a hollow-fiber membrane that has a single-layer
structure formed with a substantially single principal structural
material.

[0070] Here, a single-layer structure means being formed from a single
material. Usually, if weak materials are not strengthened through the
formation of composite materials with structural supporting bodies that
are stronger materials (ceramics, nonwoven fabrics, and the like), they
cannot be maintained in any desired shape, for example a cylinder, tube,
or the like. Consequently, in addition to the materials that form the
membrane, to maintain the desirable shape while being used as a water
treatment membrane, conventional water treatment membranes with
relatively large pore diameters are associated with tubular ceramics, or
nonwoven fabrics formed into a tubular shape, or the like, as structural
frames to support the membrane.

[0071] On the other hand, the polymer membrane for water treatment of the
present invention is formed only from a hollow-fiber membrane, and is not
accompanied by a support frame formed from different ingredients or
materials (for example, nonwoven fabric, paper, metal, ceramics, and the
like) which do not change a desirable shape such as a tube. In other
words, this means that the polymer membrane for water treatment of the
present invention is formed in a single-layer structure, and a laminated
structure using different ingredients or materials is not used.
Nevertheless, even such a structure must have sufficient strength to
maintain the desired shape such as a cylinder, tube, or the like for use
as a water treatment membrane. In other words, it has "a self-supporting
property/structure". Consequently, a support frame-less membrane with
large pore diameter can be realized. For this reason, superior water
permeability can be maintained even during backwashing, without the
portion of the membrane responsible for the filtration capability
separating from the structural support frame, which moreover differs from
tube-shaped membranes and the like that use structural support frames of
ceramics or the like.

[0072] In addition, as mentioned above, substantially single principal
structural material means that it has been formed from substantially a
single material. Substantially single material means the principal
structural material is of one type. In other words, this means that in
the material that forms the polymer membrane for water treatment (for
example, resin of which the polymer membrane for water treatment is
constituted), one type of resin accounts for 50 mass % or more
(preferably 60 mass % or more, more preferably 70 mass % or more), and
means that the properties of this one type of resin control the
properties of the structural material. Specifically, one type of resin
means a material accounting for 50 to 99 mass %.

[0073] Furthermore, for a single material and a single principal
structural material, during the manufacture of the vinyl chloride resin
described below, during the manufacture of the hollow-fiber membrane
mentioned below, the design doesn't include the additives normally used.

[0074] An example of a hollow-fiber membrane is a membrane with an outer
diameter of about 3.6 to 10 mm and a thickness of about 0.15 to 2.4 mm.

[0075] The strength of a hollow-fiber membrane is determined by various
factors such as the material, inner diameter, thickness, circularity,
internal structure, and the like, among which the use of the SDR value
(value calculated as the ratio of the outer diameter and the thickness)
was discovered to be effective. In other words, in the results from
various experiments carried out, it was found necessary to design for an
SDR value of about 34 or less to achieve a resistance to an
internal/external pressure of 0.3 MPa. On the other hand, a design in
which the SDR value was reduced was linked to a reduction in the membrane
filtration area in the water treatment module. Consequently, from the
perspective of ensuring balance therebetween, an SDR of about 3.6 or
greater is preferred.

[0076] Among these, about 4.0 or greater is preferred and about 20 or less
is preferred, and about 16 or less, or about 11 or less is further
preferred. In particular, it is preferable to establish an SDR of about 4
to 16 when the outer diameter is about 5 to 7 mm, and about 6.5 to 11 is
further preferred.

[0077] Furthermore, the inner diameter is determined by its outer diameter
and thickness, but in the example of about 1.6 to 9.4 mm, 4 mm to 8 mm is
suitable, and in this case the thickness is preferably about 0.1 mm to 2
mm.

[0078] Consequently, in concrete terms, for the polymer membrane for water
treatment of the present invention, examples include

[0079] (1) a membrane that comprises a hollow-fiber membrane having a
self-supporting structure from using a substantially single principal
structural material will have an outer diameter of 3.6 mm to 10 mm and an
SDR value of 3.6 to 34.

[0080] Among these, an outer diameter of about 5 to 7 mm and an SDR value
of about 6.5 to 11 are preferred. For this reason, the hollow-fiber
membrane maintains its strength when internal or external pressure is
applied, and a large inner diameter is maintained and the interior of the
hollow fiber does not become occluded when the water through-flow has
highly concentrated waste water.

[0081] Furthermore, the membrane inner and outer diameters, thickness, and
the like, can be measured from the actual dimensions by using electron
microphotography.

[0082] In addition, examples include (2) a membrane that comprises a
hollow-fiber membrane having a self-supporting structure from using a
substantially single principal structural material will have an inner
diameter of 3 to 8 mm and an SDR value of 4 to 13,

[0083] (3) a membrane that comprises a hollow-fiber membrane having a
self-supporting structure from using a substantially single principal
structural material will have an inner diameter of 1.6 mm to 9.4 mm, and
a thickness of 0.15 mm to 2.4 mm.

[0084] The polymer membrane for water treatment is preferably a porous
membrane having a plurality of micropores in its surface. The average
pore diameter of these micropores, for example, is about 0.001 to 10
μm, preferably about 0.01 to 1 μm. The size and density of
micropores in the membrane surface can be suitably adjusted using the
abovementioned inner diameter, thickness, the intended characteristics
and the like, for example, these can be suitable to achieve enough water
permeability as mentioned below. Thus, by such micropores being numerous,
along with serving the function of being a water permeable membrane,
using the micropore size, density, and the like can be adjusted, for
example, for the fractionation properties of an ultrafiltration membrane
or a microfiltration membrane. Furthermore, it is generally known that in
general, ultrafiltration membranes have pore sizes of about 2 to 200 nm,
while microfiltration membranes have pore sizes of about 50 nm to 10
μm.

[0085] The porosity is, for example, about 10 to 90%, and is preferably
about 20 to 80%. Here, porosity means the proportion of the total pore
area vs. the total area of the polymer membrane for water treatment from
an arbitrary horizontal cross-section (radial cross section of a hollow
fiber, same below), for example, determined by a method of calculating
the respective areas from a microphotograph of a horizontal cross-section
of the membrane.

[0086] For example, in the radial cross-section of a hollow fiber as in
the abovementioned (1),

[0087] (a) the porosity based on the cross-sectional area of the
aforementioned hollow-fiber membrane is preferably about 30 to 85%, and
about 50 to 85%, about 40 to 75%, or about 50 to 75% are further
preferred.

[0088] Additionally, (b) pores with a short axis dimension of 10 to 100
μm are preferably about 80% or more of the total pore surface area,
and about 83% or more, about 85% or more, or about 87% or more, are
further preferred.

[0089] It is furthermore preferable that, (c) there is a laminar
distribution of pores constituting the innermost layer, inner layer,
outer layer and outermost layer from the center in the radial direction,
and the long axis dimension of the pores in the aforementioned inner
layer and outer layer respectively accounts for 20 to 50% of the
thickness, while the long axis dimension of the pores in each of the
aforementioned innermost layer and outermost layer respectively accounts
for 0 to 20% of the thickness. For this reason, it is possible to
disperse the stress concentration when internal or external pressures are
applied to the hollow-fiber membrane, and to preserve the strength of the
entire membrane while preserving the water permeation properties.

[0090] In other words, in FIG. 1 that shows a radial cross-section of
hollow fiber membrane 20, pores 21 are constituted in relatively orderly
layers so that the long axis will match the radial orientation, and are
respectively arranged/distributed so as to be constituted from innermost
layer 20d, inner layer 20c, outer layer 20b, and outermost layer 20a. The
arrangement/distribution in this case can have the various layers clearly
separated and can be approximately independent, but pores 21 constituted
in one layer can be partially nested to overlap with pores 21 constituted
in another layer (see X in FIG. 1).

[0091] Furthermore, the distribution of pores in such layers can be
observed/measured using electron microphotography.

[0092] Pores 21d are distributed in innermost layer 20 of a hollow-fiber
membrane, likewise pores 21c in inner layer 20c, pores 21b in outer layer
20b, and pores 21a in outermost layer 20a, respectively. As the size of
pores 21 in each layer, for example, long axis A and/or short axis B as
shown in FIG. 1 are preferably relatively aligned for each layer within
about ±30%. In particular, the long axis dimension of pores 21c and
21b in inner layer 20c and outer layer 20b preferably amount to,
respectively, about 20 to 50% of the thickness and about 25 to 45% of the
thickness. The corresponding average long axis dimension of pores 21c and
20b, for example, are preferably relatively aligned to about ±30%, and
further preferably about ±15%. Additionally, the long axis dimension
of pores 21d and 21a in innermost layer 20d and outermost layer 20a
preferably amount respectively to about 0 to 20% of the thickness and
about 5 to 15% of the thickness. The corresponding average long axis
dimension of pores 21d and 20a, for example, are preferably relatively
aligned to about ±30%, and further preferably about ±15%.

[0093] (Ingredients/Materials)

[0094] The polymer membrane for water treatment of the present invention
is formed from a substantially single principal structural material, and
ingredients and materials used in the art can be employed as this
principal structural material, among these, vinyl chloride resins are
suitable.

[0095] Examples of vinyl chloride resins include vinyl chloride
homopolymers, copolymers of vinyl chloride monomer with copolymerizable
monomers that have an unsaturated bond, graft copolymers wherein vinyl
chloride monomer is graft copolymerized onto a polymer, (co)polymers
derived by chlorination of the vinyl chloride monomer units of such
materials, and the like. These can be used singly, or two or more types
can be combined for use. In particular, to improve the antifouling
properties, it is suitable for a hydrophilic monomer to be copolymerized.

[0096] Chlorination of the vinyl chloride monomer units can be carried out
before the polymerization or after the polymerization.

[0097] Moreover, in the case of a vinyl chloride copolymer (including
chlorinated vinyl chloride), the content of monomer units other than
vinyl chloride monomer units (including chlorinated vinyl chloride) is
within the range that does not inhibit the primary characteristics, and
is 50 mass % or more of vinyl chloride-derived units (including units
derived from chlorinated vinyl chloride), for example, a content of 50-99
mass % is preferred (the mass calculation here does not include
plasticizers in the vinyl chloride resin or other polymers that are
blended into said copolymer resin).

[0098] Other monomers or polymers can be blended into the vinyl chloride
resin. In particular, to increase the antifouling properties, it is
preferable to blend in a hydrophilic monomer-containing copolymer or a
hydrophilic polymer. In this case, the vinyl chloride resin is contained
amounts to 50 mass % or more (preferably 60 mass % or more, further
preferably 70 mass % or more) based on the total resin constituting the
membrane, and the monomer or polymer which is blended in is contained
amounts to less than 50 mass % based on the total resin constituting the
membrane.

[0099] Examples of the copolymerizable monomers, that have an unsaturated
bond, with vinyl chloride monomer include, for example,

[0107] These can be used singly, or 2 or more types can be combined for
use.

[0108] For example, it is favorable with vinyl acetate, acrylic ester,
ethylene, propylene, vinylidene fluoride to copolymerize or to blend in
order to give further flexibility and anti-pollution characteristics,
chemical resistance.

[0109] Examples of polymers that are graft-polymerized with vinyl
chloride, although not limited as long as they can be graft-polymerized
with vinyl chloride, include ethylene/vinyl acetate copolymers,
ethylene/vinyl acetate/carbon monoxide copolymers, ethylene/ethyl
acrylate copolymers, ethylene/butyl acetate/carbon monoxide copolymers,
ethylene/methyl methacrylate copolymers, ethylene/propylene copolymers,
acrylonitrile/butadiene copolymers, polyurethanes, chlorinated
polyethylene, chlorinated polypropylene, and the like. These can be used
singly, or 2 or more types can be combined for use.

[0110] Also, a crosslinkable monomer can be used as the monomer material
constituting the polymer membrane. Examples of the crosslinkable monomer
include

[0114] polyallyl compounds such as diallyl phthalate, diallyl maleate,
diallylamine, triallyl amine, triallyl ammonium salt, allyl-etherified
compounds of pentaerythritol, allyl-etherified compounds of sucrose which
has at least two allyl ether units in the molecule, and the like; and

[0123] styrene having total carbon number of 2-44 dialkyl amino group such
as dimethylamino styrene, dimethylamino methyl styrene, and the like;

[0124] vinyl pyridine such as 2- or 4-vinyl pyridine, and the like;

[0125] N-vinyl heterocyclic compounds such as N-vinyl imidazole, and the
like;

[0126] acid-neutralizing compounds of amino group-containing monomers such
as vinyl ether, for example, aminoethyl vinyl ether, dimethylamino ethyl
vinyl, or quaternized compounds in which the monomers thereof are
quaternized by halogenated alkyl (carbon number of 1-22), halogenated
benzyl, alkyl (carbon number of 1-18) or aryl (carbon number of 6-24)
sulfonic acid or dialkyl (total carbon number of 2-8) sulfate, and the
like;

[0128] Among these cationic groups, amino group-containing and ammonium
group-containing monomers are preferable.

[0129] (2) examples of the non-ionic monomer include

[0130] vinyl alcohol;

[0131] (meth)acrylic ester or (meta) acrylic amide which have a hydroxy
alkyl (carbon number of 1-8) such as the N-hydroxypropyl (meth)acrylic
amide, hydroxyethyl (meth)acrylate, N-hydroxypropyl (meta)acrylic amide,
and the like;

[0132] polyol (meth)acrylic ester such as polyethylene glycol
(meth)acrylate (a degree of polymerization of ethylene glycol: 1-30), and
the like;

[0137] N-vinyl cyclic amide such as N-vinyl pyrrolidone, and the like;

[0138] (meth)acrylic ester having alkyl (carbon number of 1-8) group such
as methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate,
and the like;

[0139] (meth)acrylic amide having cyclic amido group such as
N-(meth)acryloyl morpholine, and the like.

[0140] Among these, vinyl alcohol, (meth) acrylic amide monomer and
hydroxy alkyl group (carbon number of 1-8)-containing (meth)acrylic ester
described above, (meth) acrylic ester of polyol described above are
preferable.

[0141] (3) examples of the anionic monomer include

[0142] carboxylic acid monomer having polymeric unsaturated group such as
(meta) acrylic acid, maleic acid, itaconic acid, etc. and/or acid
anhydride (in cases where having carboxyl groups more than two in one
monomer);

[0143] sulfonic acid monomer having polymeric unsaturated group such as
styrene sulfonic acid, 2-(meth)acrylic amide-2-alkyl (carbon number of
1-4) propanesulfonic acid, and the like;

[0144] phosphate monomer having polymeric unsaturated group such as vinyl
phosphonic acid, (meth)acryloyloxy alkyl (carbon number of 1-4)
phosphoric acid, and the like.

[0145] The anionic group may be neutralized in any neutralization degree
by basic substance. In this case, all anionic groups or part of anionic
group in the polymer produce salts. Examples of a positive ion in the
salt include ammonium ion, trialkyl ammonium ion having total carbon
number of 3-54 (e.g., trimethyl ammonium ion, triethyl ammonium ion),
hydroxy alkyl ammonium ion having carbon number of 2-4, dihydroxy alkyl
ammonium ion having total carbon number of 4-8, tri hydroxy alkyl
ammonium ion having total carbon number of 6-12, alkali metal ions,
alkaline earth metals ion, and the like.

[0146] Neutralization may be performed with a monomer and after making a
polymer.

[0147] (4) Other than the vinyl monomers described above, monomers may
include a monomer having the active site that is hydrogen-bondable such
as N-vinyl-2-pyrrolidone, hydroxyethyl methacrylate, hydroxyethyl
acrylate, and the like.

[0148] Without being limiting in any particular way, any desired
conventionally-known polymerization method can be employed as the
abovementioned method for manufacturing vinyl chloride resins. Examples
thereof include bulk polymerization, solution polymerization, emulsion
polymerization, suspension polymerization, and the like.

[0149] Without being limiting in any particular way, chlorination methods
that can be used include methods that are well known in the art, such as
are described in Japanese Published Unexamined Patent Application No.
H09-278826, Japanese Published Unexamined Patent Application No.
2006-328165, World Patent WO/2008/62526, and the like. A chlorine content
of 56.7 to 73.2% in the vinyl chloride resin is preferred. A chlorine
content of 58 to 73.2% in the chlorinated vinyl chloride resin is
satisfactory, 60 to 73.2% is preferred, and 67 to 71% is further
preferred.

[0150] The degree of polymerization of the vinyl chloride resin is
preferably 250-3000, and further preferably 500-1300. If the degree of
polymerization is too low, the solution viscosity during spinning will
decrease, which will be problematic for the membrane manufacturing
operation, and the water treatment membrane made therefrom will tend to
lack strength. On the other hand, a degree of polymerization that is too
high will cause the viscosity to be too high and tends to result in
residual bubbles in the water treatment membrane that has been
manufactured. Here, the degree of polymerization means a measured value
that complies with JIS K 6720-2.

[0151] To adjust the degree of polymerization to be within the
above-mentioned range, it is preferable to make suitable adjustments to
conditions that are well known in the art, such as in reaction time,
reaction temperature, and the like.

[0152] The polymer membrane for water treatment of the present invention,
inter alia, is preferably formed from poly(vinyl chloride) (homopolymer),
poly(chlorinated vinyl chloride) (homopolymer), or copolymers of vinyl
chloride and chlorinated vinyl chloride.

[0153] However, with the goal of increasing moldability, heat stability,
or the like at forming membrane, within a range that does not damage the
effect of the present invention, additives such as lubricants, heat
stabilizing agents, membrane formation aids, or the like, can also be
blended into the vinyl chloride resin constituting the polymer membrane
for water treatment of the present invention. These can be used singly,
or two or more types can be used in combination.

[0154] Examples of lubricants include stearic acid, paraffin wax, and the
like.

[0155] Examples of heat stabilizing agents generally used in the formation
of vinyl chloride resins include tin, lead, and Ca/Zn stabilizers, and
the like.

[0156] Examples of membrane formation aids include hydrophilic polymers
such as poly(ethylene glycol), polyvinylpyrrolidone, and the like, with
various degrees of polymerization.

[0157] (Properties)

[0158] At a transmembrane pressure difference of 100 kPa, a pure water
flux of about 100 L/(m2h) or more, or about 200 L/(m2h) or more
is suitable for polymer membranes for water treatment of the present
invention, and about 600 L/(m2h) or more is preferred, about 800
L/(m2h) or more is further preferred, and about 1000 L/(m2h) or
more is still further preferred.

[0159] In addition, the membrane internal pressure resistance is
preferably about 0.3 MPa or more, and about 0.35 MPa or more or about 0.4
MPa or more is further preferred.

[0160] The external pressure resistance of the membrane is preferably
about 0.1 MPa or more, and about 0.15 MPa or more or about 0.2 MPa or
more is further preferred.

[0161] Among these, at a transmembrane pressure difference of 100 kPa, a
pure water flux of about 100 L/(m2h) or more with a membrane
internal pressure resistance of preferably about 0.3 MPa or more and
external pressure resistance of preferably about 0.1 MPa or more is
further preferred.

[0162] (Manufacturing Method)

[0163] Any of the methods for manufacturing polymer membranes for water
treatment that are well known in the art can be used, such as the
thermally-induced phase separation method (TIPS), non-solvent phase
separation method (NIPS), the drawing method, and the like. Among these,
manufacturing by the NIPS method is preferred.

[0164] For example, when employing the NIPS method, the resin solution is
prepared from a good solvent and the material (resin) that constitutes
the membrane, and optionally includes additives. Without being limiting
in any particular way, a suitable choice of a good solvent in this case
depends on the type of material (resin) or the like. Examples include
dimethyl sulfoxide, N,N-dimethylformamide, tetrahydrofuran,
N,N-dimethylacetamide, N-methyl-2-pyrrolidone, and the like.

[0165] Without being limiting the concentration and viscosity of the resin
solution in this case in any particular way, a suitable viscosity is, for
example, about 500-4000 mPas, and about 1000-3000 mPas is preferred. In
this manner, it is possible to maintain the external circular shape of
the hollow-fiber membrane in the spinning line, and a membrane of a
uniform gauge and thickness can be manufactured.

[0166] Moreover, from another perspective, a preparation exhibiting a
difference in specific gravity with a non-solvent mentioned below of
within 1.0 is suitable, and it is preferably within 0.8, and further
preferably within 0.2. In this manner, with the membrane itself floating
or submerged in the coagulation tank, it is possible to effectively
prevent the membrane from being flattened while being taken up.

[0167] To coagulate the abovementioned resin solution, normally,
coagulation tank 30 as shown in FIG. 4 is used. Coagulation tank 30 is
filled with a non-solvent.

[0168] Usually, to spin a resin solution, the spinneret used is equipped a
discharge port having a concentrically-arranged double nozzle. This
spinneret can be positioned inside or outside the coagulation tank, or
extends from outside to inside to be able to spin into coagulation tank
30. For example, spinneret 31 provided with a discharge port (not shown
in the figure) is positioned inside coagulation tank 30, in other words,
immersed in non-solvent. In this manner, when spinneret 31 is positioned
inside coagulation tank 30, the resin solution does not come into contact
with air and is discharged directly into non-solvent, and since a
liquid-liquid phase separation is initiated rapidly, giving a porous
surface with no dense skin layer is produced on the surface.
Specifically, superior water permeability is exhibited due to the
reduction in filtration resistance. In addition, even with the spinning
oriented horizontally as mentioned below, according to the design of the
present invention with the spinneret immersed in the coagulation tank,
for the normal continuous discharge of the resin solution, submerging the
spinneret in the coagulation tank following the previous condition of the
resin solution being discharged into the air can avoid the clogging
associated with increased discharge resistance produced at the nozzle tip
during initial spinning.

[0169] Even when the spinneret is positioned horizontally outside the
coagulation tank, spinning can be oriented horizontally in the same
manner as described in the present invention, and in this case the two
procedures below for initiating spinning can be considered. For example,
(1) a method wherein when non-solvent flows out continuously from an
opening part in the side of the coagulation tank, the discharge port of
the spinneret is introduced while resin solution is being discharged and
the resin solution is guided into the coagulation tank, and (2) a method
wherein the discharge port of the spinneret is positioned or fixed in the
side of the coagulation tank beforehand after which discharge of the
resin solution begins, and the resin solution is discharged into the
coagulation tank.

[0170] In (1), the non-solvent flow and the flow of the resin solution
from the discharge port of the spinneret are oriented in opposite
directions, and the resin solution discharged from the spinneret
discharge port experiences substantial discharge resistance when spinning
is initiated. For this reason, congestion of the flow occurs in the
vicinity of the spinneret discharge port, and this portion of the resin
progressively solidifies, resulting in a high likelihood of occlusion in
the spinneret discharge port.

[0171] In (2), the non-solvent in the coagulation tank prior to the start
of spinning backwashes the spinneret discharge port through which resin
solution should flow, and there is a high likelihood the resin solution
will solidify in the spinneret discharge port part when spinning begins.

[0172] The result is that when the present invention is practiced
industrially, there will be a significant reduction in workability when
membrane manufacture begins. Additionally, a total or partial clogging in
the discharge port by residues will interfere with the normal formation
of the membrane, which is considered to cause a decrease in strength and
a decrease in water permeability as a result. In light of this
information, and taking into account the results of diligent study, the
present inventors identified the most suitable procedure for immersion of
the spinneret (discharge port) in the coagulation tank as an embodiment
of the present invention.

[0173] The direction of discharge (FIG. 3, 32) of the resin solution from
spinneret 31, in other words the direction in which the resin solution is
expelled from the discharge port, for example, is preferably adjusted to
be within ±30° (FIG. 3, 33) with respect to bottom 30a of
coagulation tank 30. In other words, it is preferable for the resin
solution to be discharged such that the direction of discharge is
adjusted to be within ±30° with respect to the ground. Among
these, it is further preferable to make adjustment such that the
discharge is horizontal or nearly horizontal (about)±5° with
respect to coagulation tank 30a or the ground.

[0174] Heretofore, the system generally adopted has the resin solution
discharged vertically from a spinneret, and since the overall outer
diameter is less in the case of conventional hollow-fiber membranes, and
conforms relatively flexibly even when the machine direction is changed,
and thus doesn't cause deformation of the membrane such as flattening or
bending.

[0175] On the other hand, according to the study by inventors up to the
present, for polymer membranes for water treatment within the SDR value
range that appears in the present invention to achieve a large outer
diameter compared to conventional hollow-fiber membranes, in a discharge
system with an angle in the aforementioned vertical direction or that
exceeds the range shown in the present invention, serious shape defects
such as membrane flattening and bending occur, and a significant
reduction in strength will take place due to being overwhelmed by the
already flexible condition of the polymer membrane for water treatment
during solidification toward changes in the spinning direction. In
addition to the abovementioned factual diligent study, the present
inventors identified the most suitable procedure for carrying out
spinning would be when, during the manufacture of the polymer membrane
for water treatment shown in the present invention, the resin solution is
discharged from a spinneret in a horizontal direction and the spinneret
is immersed in a coagulation tank.

[0176] In other words, within the SDR value range shown in the present
invention, wherein serious shape defects such as flattening of the
membrane or bending are avoided, a single-layer membrane without having a
support frame would have superior strength and water permeability, so
that a polymer membrane for water treatment could be manufactured wherein
the membrane terminus would not become clogged even with highly
concentrated wastewater such as in bio-treated wastewater, and spinning
can take place in the horizontal direction from a spinneret immersed in
water.

[0177] The non-solvent with which the coagulation tank is filled can be
suitably selected according to the abovementioned types of resin
solution, for example, having water as a principal ingredient is
preferred.

[0178] Since the non-solvent in the coagulation tank comes into direct
contact with the resin solution, the difference in temperature between
the resin solution discharged from the discharge port (or spinneret) and
the non-solvent is preferably within about 100° C. In this manner,
it is possible to avoid clogging in the vicinity of the spinneret
discharge port due a sharp decrease in the temperature of the resin
solution and a rapid increase in viscosity of the resin solution
associated with a sharp decrease in the temperature of the resin
solution. Additionally, by keeping the non-solvent at a fixed
temperature, it is possible to maintain stable phase separation behavior
in the resin solution, which can be manifested in stable properties such
as water permeability and strength.

[0179] The take-up of the membrane during membrane manufacture generally
is preferably carried out with a linear orientation. In the present
invention, as mentioned above, by keeping the discharge port within
±30° of horizontal within the coagulation tank, there will be
no change in the membrane take-up direction after the resin solution is
discharged, and take-up will be easy while maintaining a fixed speed and
uniform load. In this way, it is possible to minimize deformations in the
membrane structure.

[0180] Cutting of the membrane after take-up can be done either inside or
outside the coagulation tank. In particular, as shown in FIG. 4, when the
cutting of membrane 34 occurs outside coagulation tank 30, cutting 35 is
preferably carried out at cutting position 38 higher than position 37 of
the discharge port of spinneret 31 in coagulation tank 30. In this
manner, flow of the internal coagulation liquid from the tips of the
discharged membrane due to siphoning effects will be prevented, which
will minimize pressure changes in the internal coagulation liquid inside
the membrane, and prevent not only flattening of the membrane shape but
also variations in shape, which will have the effect of stabilizing the
membrane shape. From this perspective, when cutting is carried out inside
the coagulation tank, there is no particular limitation concerning this
cutting position.

[0181] The polymer membrane for water treatment of the present invention
has a superior balance between water permeability and physical strength.
Consequently, when suitably employed as a separation membrane in existing
water treatment systems, it enables suitable water treatment with the
goal of water purification, and in particular the treatment of highly
concentrated waste water. The polymer membrane for water treatment of the
present invention having such characteristics can be suitably employed as
and ultrafiltration (UF) membrane and a microfiltration (MF) membrane.

[0182] Although not limiting in any particular way, in addition to using
the abovementioned polymer membrane for water treatment of the present
invention, and depending on its object, purpose, and the like, the water
treatment method of the present invention can be realized using any
method well known in the art.

[0183] Examples include the use of immersion MBRs (membrane bioreactor
method) that is being increasing adopted in recent years, wherein in this
case, wastewater drawn in by pump undergoes biological treatment using
activated sludge from an activated sludge treatment tank in units
employing a hollow-fiber-shaped water treatment membrane. Here, the flow
is introduced to the interior of the polymer membrane for water treatment
shown in the present invention that is accommodated inside the unit, and
water treatment can take place by inner pressure filtration by applying
pressure from the inside of the membrane to the outside.

[0184] Moreover, for example, the use of the inside-out-type MBR shown in
FIG. 2 is advantageous. For example, the method of separating water by
passage of activated sludge through the hollow fibers of a polymer
membrane for water treatment can be used. Specifically, an example of the
separation method with activated sludge is shown, wherein wastewater is
sequentially fed into anaerobic tank 11 as shown by arrow A and then into
activated sludge tank 12, and after a predetermined purification in
activated sludge tank 12, the activated sludge including the treated
water is pumped out as shown by arrow B, and using water treatment module
10 with its ends sealed with sealing material 14 having a multiplicity of
hollow-fiber water treatment membranes 13 accommodated in a circular
casing, a water flow with a pressure load of 0.3 MPa or more of activated
sludge containing treated water passes into the interior of the hollow
fibers in hollow-fiber treatment membrane 13, with the treated water
shown by arrow D passing through the hollow-fiber membrane and being
separated. Furthermore, the separated sludge returns to activated sludge
tank 12 as shown by arrow C, and is reused. The activated sludge
concentration is preferably 3,000 ppm to 12,000 ppm.

[0185] The polymer membrane for water treatment according to the present
invention will have a large inner diameter compared to conventional
hollow-fiber membranes for water treatment while maintaining adequate
strength, and when conducting an inside-out filtration of waste water
with a comparatively high floc content such as bio-treated wastewater,
the membrane end surface, in other words the membrane at the intake port
where the wastewater is introduced, cannot become clogged. This is a
characteristic that is not observed in conventional hollow-fiber-type
membranes for water treatment.

WORKING EXAMPLES

[0186] Polymer membranes for water treatment and methods for their
manufacture of the present invention are described in detail below based
on working examples. Furthermore, the present invention is not limited in
any way to these working examples.

Working Example 1

[0187] <<Membrane Manufacture>>

[0188] 25 wt % chlorinated vinyl chloride resin (Sekisui Chemical Co.,
HA31K; degree of chlorination: 67%; degree of polymerization: 800) and 20
wt % poly(ethylene glycol) 400 as a pore formation aid were dissolved in
dimethylacetamide. This resin solution was discharged continuously in a
substantially level manner into a coagulation tank (filled with water)
using a spinneret, and a porous hollow-fiber membrane was obtained due to
phase separation in the coagulation tank.

[0189] As shown in FIG. 4, the spinning direction of membrane 34 was
oriented to the horizontal, and in coagulation tank 30 (filled with
water), 10 m was taken up in a straight line along the horizontal
direction 36 from the discharge port of spinneret 31. Within about 1 m
downstream therefrom, membrane 34 is raised up about 10 cm by roller 39,
and cutting 35 is made by a cutting machine outside coagulation tank 30
and at cutting position 38 higher than position 37 of the discharge port
of spinneret 31 which is inside coagulation tank 30.

[0190] <<Strength Evaluation>>

[0191] The membrane obtained has an outer diameter of 5.4 mm, and SDR
value of 18 (inner diameter: 4.8 mm), and is of uniform shape without any
cracks, bends, swelling, warping, or uneven thicknesses.

[0193] Additionally, the tensile strength was 33 N/fiber, and the tensile
elongation at break was 50%.

[0194] In a radial cross-section, the proportion of surface area accounted
for by pores was 75%. The pores in the outermost layer and innermost
layer, respectively, had a width (length along the short axis direction;
B in FIG. 1) of 10 μm, and the length (length along the long axis
direction; A in FIG. 1) was 5% of the thickness. In the outer layer and
inner layer, respectively, the width was 20 μm and the length was 40%
of the thickness. Such pores, in other words, pores with a short axis
dimension of 10-100 μm, will have a sum total of cross-sectional
surface area for all pores of about 85%.

[0195] <<Evaluation of Water Permeability>>

[0196] A hollow-fiber membrane single fiber was used to manufacture a
water treatment module as shown in FIG. 2, and a pure water flux of 200
L/m2hratm was confirmed.

[0197] In addition, when a water permeability test was conducted using the
device shown in FIG. 2 using activated sludge with an MLSS of 3000, a
water permeability of 150-100 L/m2hratm was confirmed including the
backwashing process. In the same manner, a water permeability of 180-150
L/m2hratm was confirmed for industrial wastewater with an SS of
about 50.

[0198] Furthermore, bio-treated water with an MLSS of about 3000 means
3,000 mg/L of activated sludge suspended solids, while industrial
wastewater with an SS of about 50 means 50 mg/L suspended solids.

[0199] Additionally, when filtration was carried out at 25° C.
using an aqueous solution with a γ-globulin concentration of 100
ppm at 0.05 MPa internal pressure during treatment, the relative water
permeability compared to pure water flux was about 80%. In this case, the
globulin blocking rate was 99% or greater.

[0200] From the above results, in spite of the large aperture diameter,
while the polymer membrane for water treatment of the present invention
maintained an adequate internal and external water pressure resistance
strength, a mechanical strength of 0.3 MPa or greater and water
permeability of 100 L/m2hratm, in particular a superior balance
between water permeability and tensile strength was confirmed. In
addition, occlusion due the deposition of solids is unlikely to occur,
and it has been demonstrated that filtration is possible without
pre-processing such as pre-filtration, precipitation, or the like, in the
treatment of high-SS (high suspended solids) wastewater.

Working Example 2

[0201] <<Membrane Manufacture>>

[0202] 25 wt % chlorinated vinyl chloride resin (Sekisui Chemical Co.,
HA31K; degree of chlorination: 67%; degree of polymerization: 800) and 20
wt % poly(ethylene glycol) 400 as a pore formation aid were dissolved in
tetrahydrofurane. This resin solution was discharged continuously in a
substantially level manner into a coagulation tank (filled with water)
using a spinneret, and a porous hollow-fiber membrane was obtained due to
phase separation in the coagulation tank.

[0203] As shown in FIG. 4, the spinning direction of membrane 34 was
oriented to the horizontal, and in coagulation tank 30 (filled with
water), 10 m was taken up in a straight line along the horizontal
direction 36 from the discharge port of spinneret 31. Within about 1 m
downstream therefrom, membrane 34 is raised up about 10 cm by roller 39,
and cutting 35 is made by a cutting machine outside coagulation tank 30
and at cutting position 38 higher than position 37 of the discharge port
of spinneret 31 which is inside coagulation tank 30.

[0204] <<Strength Evaluation>>

[0205] The membrane obtained has an outer diameter of 5.1 mm, and SDR
value of 8.5, and is of uniform shape without any cracks, bends,
swelling, warping, or uneven thicknesses.

[0207] Additionally, the tensile strength was 45 N/fiber, and the tensile
elongation at break was 50%.

[0208] <<Evaluation of Water Permeability>>

[0209] A hollow-fiber membrane single fiber was used to manufacture a
water treatment module as shown in FIG. 2, and a pure water flux of 120
L/m2hratm was confirmed.

[0210] In addition, when a water permeability test was conducted using the
device shown in FIG. 2 using activated sludge with an MLSS of 3000, a
water permeability of 100-50 L/m2hratm was confirmed including the
backwashing process. In the same manner, a water permeability of 110-80
L/m2hratm was confirmed for industrial wastewater with an SS of
about 50.

[0211] When filtration was carried out at 25° C. using an aqueous
solution with a γ-globulin concentration of 100 ppm at 0.05 MPa
internal pressure during treatment, the relative water permeability
compared to pure water flux was about 80%. In this case, the globulin
blocking rate was 99% or greater.

Working Example 3

[0212] <<Membrane Manufacture>>

[0213] 22 wt % chlorinated vinyl chloride resin (Sekisui Chemical Co.,
HA05K; degree of chlorination: 67%; degree of polymerization: 500) and 22
wt % poly(ethylene glycol) 400 as a pore formation aid were dissolved in
dimethylacetamide. This resin solution was discharged continuously in a
substantially level manner into a coagulation tank (filled with water)
using a spinneret, and a porous hollow-fiber membrane was obtained due to
phase separation in the coagulation tank.

[0214] As shown in FIG. 4, the spinning direction of membrane 34 was
oriented to the horizontal, and in coagulation tank 30 (filled with
water), 10 m was taken up in a straight line along the horizontal
direction 36 from the discharge port of spinneret 31. Within about 1 m
downstream therefrom, membrane 34 is raised up about 10 cm by roller 39,
and cutting 35 is made by a cutting machine outside coagulation tank 30
and at cutting position 38 higher than position 37 of the discharge port
of spinneret 31 which is inside coagulation tank 30.

[0215] <<Strength Evaluation>>

[0216] The membrane obtained has an outer diameter of 4.6 mm, and SDR
value of 5.8, and is of uniform shape without any cracks, bends,
swelling, warping, or uneven thicknesses.

[0218] Additionally, the tensile strength was 40 N/fiber, and the tensile
elongation at break was 50%.

[0219] <<Evaluation of Water Permeability>>

[0220] A hollow-fiber membrane single fiber was used to manufacture a
water treatment module as shown in FIG. 2, and a pure water flux of 450
L/m2hratm was confirmed.

[0221] In addition, when a water permeability test was conducted using the
device shown in FIG. 2 using activated sludge with an MLSS of 3000, a
water permeability of 300-200 L/m2hratm was confirmed including the
backwashing process. In the same manner, a water permeability of 400-300
L/m2hratm was confirmed for industrial wastewater with an SS of
about 50.

[0222] When filtration was carried out at 25° C. using an aqueous
solution with a γ-globulin concentration of 100 ppm at 0.05 MPa
internal pressure during treatment, the relative water permeability
compared to pure water flux was about 80%. In this case, the globulin
blocking rate was 99% or greater.

Comparative Example 1

High SDR

[0223] <<Membrane Manufacture>>

[0224] 25 wt % chlorinated vinyl chloride resin (Sekisui Chemical Co.,
HA31K; degree of chlorination: 67%; degree of polymerization: 800) and 20
wt % poly(ethylene glycol) 400 as a pore formation aid were dissolved in
dimethylacetamide. This resin solution was discharged continuously in a
substantially level manner into a coagulation tank (filled with water)
using a spinneret, and a porous hollow-fiber membrane was obtained due to
phase separation in the coagulation tank.

[0225] As shown in FIG. 4, the spinning direction of membrane 34 was
oriented to the horizontal, and in coagulation tank 30 (filled with
water) 10 m was taken up in a straight line along the horizontal
direction 36 from the discharge port of spinneret 31. Within about 1 m
downstream therefrom, membrane 34 is raised up about 10 cm by roller 39,
and cutting 35 is made by a cutting machine outside coagulation tank 30
and at cutting position 38 higher than position 37 of the discharge port
of spinneret 31 which is inside coagulation tank 30.

[0226] <<Strength Evaluation>>

[0227] The membrane obtained has an outer diameter of 5.1 mm, and SDR
value of 40, and is of uniform shape without any cracks, bends, swelling,
warping, or uneven thicknesses.

[0228] However, the pressure resistance was, internal pressure: 0.2 MPa;
outer pressure: 0.08 MPa, and the properties of a water treatment
membrane could not be demonstrated.

Comparative Example 2

Vertical Extrusion

[0229] <<Membrane Manufacture>>

[0230] 25 wt % chlorinated vinyl chloride resin (Sekisui Chemical Co.,
HA31K; degree of chlorination: 67%; degree of polymerization: 800) and 20
wt % polyethylene glycol) 400 as a pore formation aid were dissolved in
dimethylacetamide. This resin solution was discharged continuously
substantially in a vertical manner into a coagulation tank (filled with
water) using a spinneret, and a porous hollow-fiber membrane was obtained
due to phase separation in the coagulation tank.

[0231] As shown in FIG. 5, with a vertical spinning orientation, membrane
40a is introduced into coagulation tank 30 (filled with water) through a
3 cm air gap, and 1 meter downstream from the spinneret, the machine
direction for membrane 40a is changed by 300° using guide roller
41, and then again the machine direction of membrane 40b is changed by
30° using guide roller 42, and take-up is in a straight line of
about 8 m. At about 1 m downstream therefrom, membrane 34 is raised up
about 10 cm by roller 39, and cutting 35 is made by a cutting machine
outside coagulation tank 30 and at cutting position 38 higher than
position 37 of the discharge port of spinneret 31 inside coagulation tank
30.

[0232] <<Strength Evaluation>>

[0233] The membrane obtained has an outer diameter of 5.4 mm, and SDR
value of 18, and the shape is non-uniform with cracks, bends, swelling,
warping, and uneven thicknesses.

[0234] Working Examples 1 to 3 and Comparative Examples 1 to 2 are
illustrated in Table 1.

[0236] 18 wt % chlorinated vinyl chloride resin (Sekisui Chemical Co.,
HA31K; degree of chlorination: 67%; degree of polymerization: 800) and 15
wt % polyvinylpyrrolidone as a pore formation aid were dissolved in
dimethylacetamide. This resin solution was discharged continuously in a
substantially level manner into a coagulation tank (filled with water)
using a spinneret, and a porous hollow-fiber membrane was obtained due to
phase separation in the coagulation tank.

[0237] As shown in FIG. 4, the spinning direction of membrane 34 was
oriented to the horizontal, and in coagulation tank 30 (filled with
water), 10 m was taken up in a straight line along the horizontal
direction 36 from the discharge port of spinneret 31. Within about 1 m
downstream therefrom, membrane 34 is raised up about 10 cm by roller 39,
and cutting 35 is made by a cutting machine outside coagulation tank 30
and at cutting position 38 higher than position 37 of the discharge port
of spinneret 31 which is inside coagulation tank 30.

[0238] <<Strength Evaluation>>

[0239] The membrane obtained has an outer diameter of 5.6 mm, and SDR
value of 11.2, and is of uniform shape without any cracks, bends,
swelling, warping, or uneven thicknesses.

[0242] A hollow-fiber membrane single fiber was used to manufacture a
water treatment module as shown in FIG. 2, and a pure water flux of 300
L/m2hratm was confirmed.

[0243] In addition, when a water permeability test was conducted using the
device shown in FIG. 2 using activated sludge with an MLSS of 3000, a
water permeability of 150-100 L/m2hratm was confirmed including the
backwashing process. In the same manner, a water permeability of 250-200
L/m2hratm was confirmed for industrial wastewater with an SS of
about 50.

[0244] When filtration was carried out at 25° C. using an aqueous
solution with a γ-globulin concentration of 100 ppm at 0.05 MPa
internal pressure during treatment, the relative water permeability
compared to pure water flux was about 80%. In this case, the globulin
blocking rate was 99% or greater.

[0245] These results are illustrated in Table 2.

Working Example 5

CA

[0246] <<Membrane Manufacture>>

[0247] 24 wt % cellulose triacetate and 15.4 wt % triethylene glycol as a
pore formation aid were dissolved in N-methyl-2-pyrrolidone. This resin
solution was discharged continuously in a substantially level manner into
a coagulation tank (filled with water) using a spinneret, and a porous
hollow-fiber membrane was obtained due to phase separation in the
coagulation tank.

[0248] As shown in FIG. 4, the spinning direction of membrane 34 was
oriented to the horizontal, and in coagulation tank 30 (filled with
water), 10 m was taken up in a straight line along the horizontal
direction 36 from the discharge port of spinneret 31. Within about 1 m
downstream therefrom, membrane 34 is raised up about 10 cm by roller 39,
and cutting 35 is made by a cutting machine outside coagulation tank 30
and at cutting position 38 higher than position 37 of the discharge port
of spinneret 31 which is inside coagulation tank 30.

[0249] <<Strength Evaluation>>

[0250] The membrane obtained has an outer diameter of 5.6 mm, and SDR
value of 11.2, and is of uniform shape without any cracks, bends,
swelling, warping, or uneven thicknesses.

[0253] A hollow-fiber membrane single fiber was used to manufacture a
water treatment module as shown in FIG. 2, and a pure water flux of 700
L/m2hratm was confirmed.

[0254] In addition, when a water permeability test was conducted using the
device shown in FIG. 2 using activated sludge with an MLSS of 3000, a
water permeability of 400-300 L/m2hratm was confirmed including the
backwashing process. In the same manner, a water permeability of 600-500
L/m2hratm was confirmed for industrial wastewater with an SS of
about 50.

[0255] When filtration was carried out at 25° C. using an aqueous
solution with a γ-globulin concentration of 100 ppm at 0.05 MPa
internal pressure during treatment, the relative water permeability
compared to pure water flux was about 80%. In this case, the globulin
blocking rate was 99% or greater.

[0256] These results are illustrated in Table 2.

Working Example 6

PES

[0257] <<Membrane Manufacture>>

[0258] 22 wt % polyether sulfone and 5 wt % polyvinylpyrrolidone as a pore
formation aid were dissolved in N-methyl-2-pyrrolidone. This resin
solution was discharged continuously in a substantially level manner into
a coagulation tank (filled with water) using a spinneret, and a porous
hollow-fiber membrane was obtained due to phase separation in the
coagulation tank.

[0259] As shown in FIG. 4, the spinning direction of membrane 34 was
oriented to the horizontal, and in coagulation tank 30 (filled with
water), 10 m was taken up in a straight line along the horizontal
direction 36 from the discharge port of spinneret 31. Within about 1 m
downstream therefrom, membrane 34 is raised up about 10 cm by roller 39,
and cutting 35 is made by a cutting machine outside coagulation tank 30
and at cutting position 38 higher than position 37 of the discharge port
of spinneret 31 which is inside coagulation tank 30.

[0260] <<Strength Evaluation>>

[0261] The membrane obtained has an outer diameter of 5.6 mm, and SDR
value of 11.2, and is of uniform shape without any cracks, bends,
swelling, warping, or uneven thicknesses.

[0264] A hollow-fiber membrane single fiber was used to manufacture a
water treatment module as shown in FIG. 2, and a pure water flux of 300
L/m2hratm was confirmed.

[0265] In addition, when a water permeability test was conducted using the
device shown in FIG. 2 using activated sludge with an MLSS of 3000, a
water permeability of 200-150 L/m2hratm was confirmed including the
backwashing process. In the same manner, a water permeability of 250-200
L/m2hratm was confirmed for industrial wastewater with an SS of
about 50.

[0266] When filtration was carried out at 25° C. using an aqueous
solution with a γ-globulin concentration of 100 ppm at 0.05 MPa
internal pressure during treatment, the relative water permeability
compared to pure water flux was about 80%. In this case, the globulin
blocking rate was 99% or greater.

[0269] 18 wt % chlorinated vinyl chloride resin (Sekisui Chemical Co.,
HA31K; degree of chlorination: 67%; degree of polymerization: 800) and 15
wt % polyvinylpyrrolidone as a pore formation aid were dissolved in
dimethylacetamide. This resin solution was discharged continuously in a
substantially level manner into a coagulation tank (filled with water)
using a spinneret, and a porous hollow-fiber membrane was obtained due to
phase separation in the coagulation tank. At that time, discharge rate of
the resin solution, discharge rate of the inner coagulation solution,
taking up speed, and the like are changed and membranes of various shape
were made.

[0270] As shown in FIG. 4, the spinning direction of membrane 34 was
oriented to the horizontal, and in coagulation tank 30 (filled with
water), 10 m was taken up in a straight line along the horizontal
direction 36 from the discharge port of spinneret 31. Within about 1 m
downstream therefrom, membrane 34 is raised up about 10 cm by roller 39,
and cutting 35 is made by a cutting machine outside coagulation tank 30
and at cutting position 38 higher than position 37 of the discharge port
of spinneret 31 which is inside coagulation tank 30.

[0271] <<Strength Evaluation>>

[0272] The membranes obtained have an outer diameter of 3.8-10 mm, and SDR
value of 7-16, and is of uniform shape without any cracks, bends,
swelling, warping, or uneven thicknesses.

[0275] A hollow-fiber membrane single fiber was used to manufacture a
water treatment module as shown in FIG. 2, and a pure water flux of 300
L/m2hratm was confirmed for all membranes.

[0276] In addition, when a water permeability test was conducted using the
device shown in FIG. 2 using activated sludge with an MLSS of 3000, a
water permeability of 200-150 L/m2hratm was confirmed including the
backwashing process. In the same manner, a water permeability of 250-300
L/m2hratm was confirmed for industrial wastewater with an SS of
about 50.

[0277] A hollow-fiber membrane was manufactured using the same method as
in Working Example 1 except that after take-up of the membrane in the
horizontal direction, the height of the membrane was not changed but
remained as is for the cutting made by the cutting machine in the
coagulation tank.

[0278] The results were confirmed as exhibiting substantially the same
characteristics as in Working Example 1.

Working Example 16

Upward 20°

[0279] A hollow-fiber membrane was manufactured using the same method as
in Working Example 1 except that the membrane spinning direction was
upward 20°, the membrane was taken up in a straight line, and the
cutting was made in the coagulation tank without changing the existing
orientation or height. The results were confirmed as exhibiting
substantially the same characteristics as in Working Example 1.

Working Example 17

Downward 20°

[0280] A hollow-fiber membrane was manufactured using the same method as
in Working Example 1 except that membrane spinning direction was downward
20°, the membrane was taken up in a straight line, and the cutting
was made in the coagulation tank without changing the existing
orientation or height. The results were confirmed as exhibiting
substantially the same characteristics as in Working Example 1.

Comparative Example 3

Upward of 45°

[0281] A hollow-fiber membrane was manufactured using the same method as
in Working Example 1 except that membrane spinning direction was upward
45°, the membrane was taken up in a straight line, and the cutting
was made in the coagulation tank without changing the existing
orientation or height. However, the membrane obtained has the shape that
is non-uniform with swelling, warping, and uneven thicknesses relative to
Working Example 1.

Comparative Example 4

Downward 45°

[0282] A hollow-fiber membrane was manufactured using the same method as
in Working Example 1 except that membrane spinning direction was downward
45°, the membrane was taken up in a straight line, and the cutting
was made in the coagulation tank without changing the existing
orientation or height. However, the membrane obtained has the shape that
is non-uniform with swelling, warping, and uneven thicknesses relative to
Working Example 1.

INDUSTRIAL APPLICABILITY

[0283] Regardless of aspect of a water treatment device, the present
invention can be widely-used as a membrane for water treatment and a
microfiltration membrane for purifying water, such as for removing
turbidity from river water and groundwater, clarification of industrial
water, treatment of wastewater and sewage, and as a pretreatment for
seawater desalination, and the like, in particular, it is used with
advantage for MBR.